Life Boat

[sankar_mariner]

Please explain how the life boat is protected from falling back into the water
if the power fails when hoisting the lifeboat.


Thanks.

[JK]

Centrifugal brake

[sankar_mariner]

but centrifugal brake is fitted to restrict the speed of descent to 36 m/min.
which is a safety feature incorporated to prevents the operator from lowering the life boat too quickly.

[JollyJack]

dog clutch, gearbox, motor etc. Centrifugal brake works when the dog clutch is taken out and the drum is free.

[Big Pete]

Hi Sankar,

In my opinion JK made a mistake there, probably too distracted by the day job.

The centrifugal brake is designed to brake harder the faster the boat is descending and maintain a constant, safe, rate of descent, as you say.

Unfortunatly there are lots of different designs of Davit around nowadays......
Some are still fitted with a "Deadman's Handle" type of Brake. This has a lever that has to be lifted to disengage the brake and allow the boat to descend. The lever is fitted with a heavy weight that will pull the brake on if the handle is released.
By use of ratchets an Electric motor can hoist the boat up, while the brake will prevent it falling.

Others are Hydraulically operated and the system is designed to "Fail Safe" so that the boat will stop if there is any loss of Hydraulic pressure. Similar to cranes.

A lot of Electric motors on Cranes, windlasses, ER hoists, hatch covers etc are fitted with an electromagnetic Brake. These are spring loaded into the on position. When power is applied to the motor a coil is energised pulling the brake off. This ensures that the motor can only turn under power.

BP

[JK]

you are generous BP! LOL. I stand corrected.

That was 2 wrong posts in one day. I need to do more operational work.

[jimmys]

The last life boat I was involved in was the 150 person tested on the Clyde. Two crew and 148 punters. Launched by gravity from inside the boat at the con position, two levers one releases the dead man brake and the other the hooks. When the boat is lowered she comes into the embarkation position automatically. When she is in position he puts the dead man brake on. Load up the punters. When loaded he commences the drop to the water. Speed is controlled by the centrifugal brake, only speed is controlled by this brake it cannot stop the full loaded boat, if he wants a stop he uses the dead man brake. The reason for this is the two brakes are positioned differently in the gearing. He drops to position and fires the hooks and the boat drops to the sea.
It is retrieved by air and the motor is attached to a square shaft which drives thro' the dead man brake on to the gearing if the motor fails, as it only retrieves, the dead man brake comes on automatically and locks the boat in position. The dead man brake does not work on retrieve only drop. The air motor does not have sufficient speed on retrieve so no centrifugal brake on retrieve.
First set of reductions planetary gearing and second set spurs, dead mans brake in first set of reductions and centrifugal in the spurs.
Punters were UKmarines from Arbroath and it was done well within the 30 minutes. The only problem is it is three storey perches like parrots and if you are prone to seasickness don't go on the top perch.
A wee bit more money spent on the Concordia like this boat and they would have got them all away. A good passenger ship lifeboat. Big Volvo engine goes at twenty knots.

regards
jimmy

[JollyJack]

I tried several times to post exerpts from the LSA code here regarding launching arrangements, but got:

General Error
SQL ERROR [ mysql4 ]

Incorrect string value: '\xF4\x80\x82\x99 a...' for column 'post_text' at row 1 [1366]

An SQL error occurred while fetching this page. Please contact the Board Administrator if this problem persists.
Please notify the board administrator or webmaster: martin@dieselduck.net

Lets see if this does the same.

The web pages are:

http://www.pomorci.com/Propisi/80-100/L ... ocevic.pdf

http://www.imo.org/MediaCentre/PressBri ... ition.aspx

http://www.imo.org/Publications/Documen ... ID982E.pdf

[JK]

Posting this for Jolly Jack:
(Theres a wee glich in the works )

Here's a guide to the Life Saving Appliances Code, empowered by SOLAS.

http://www.pomorci.com/Propisi/80-100/L ... ocevic.pdf

Section 10 is of interest and says:

"The speed at which the fully loaded survival craft or rescue boat is lowered to the water shall not be less than that obtained from the formula:
S = 0.4 + 0.02H where S is the lowering speed in meters per second and H is the height in meters from the davit head to the waterline with the ship at the lightest sea-going condition.

The maximum lowering speed shall be established by the Administration having regard to the design of the survival craft or rescue boat.

and

"The launching mechanism shall be so arranged that it may be actuated by one person from a position on the ship's deck and, except for secondary launching appliances for free-fall lifeboats, from a position within the survival craft or rescue boat. When launched by a person on the deck, the survival craft or rescue boat shall be visible to that person.

The winch brakes of a launching appliance shall be of sufficient strength to withstand:
a static test with a proof load of not less than 1.5 times the maximum working load;
a dynamic test with a proof load of not less than 1.1 times the maximum working load at maximum lowering speed.

("Dynamic test" is stopping the boat while lowering fully loaded at the recommended speed.)

An efficient hand gear shall be provided for recovery of each survival craft and rescue boat."
"

A supplement dealing with release mechanisms was added in 2012:

http://www.imo.org/Publications/Documen ... ID982E.pdf

The Code may be bought from IMO here:

http://www.imo.org/MediaCentre/PressBri ... ition.aspx

[The Dieselduck]

"General Error", hey, who stole my morning alarm clock noise maker! I seem to get those in numerous areas, most of which are offline, ehehehee.

I haven't got a clue why you specifically got that message, but the upload attachment feature has caused me a bit of headaches, damn free software... (actually it works better than some stuff I pay for), anyways, its been a bit of a learning curve, generally its because of some limit reached, but I increase the size limits some time back, but maybe its not enough.

Let me try...

Ooooooooh I think I see the problem. Its not size, its the format. You may have been trying to upload a file that is not acceptable to the server (usually my choice) due to possibility of computer exploitation - which I would rather not be cursed by you for it.

ID982E.pdf

(107.63 KiB) Downloaded 807 times

LSA code basic - by Capt. Brakocevic.pdf

(1004.97 KiB) Downloaded 536 times

[The Dieselduck]

That's reminds me, I hate the fact that the IMO does not freely distribute the electronic format of their rules. Most seafarers don't make enough in a month wages to afford a copy of the rules that dictate their work, seems very strange...

...and another thing, that guide from the Captain is actually very good reference to have in ones arsenal.

[JK]

There were 2 bullets in the text body that threw the server into a tizzy. Once they were gone everything worked fine.

[JK]

I once went through the exercise of deciding whether we could take an old rule davit from one ship and put it on another ship that also had old rule davits as a second set.
(BTW, TC won't allow it, once you take the grandfathered or old rule original equipment off, new rule equipment has to go on.)

After lengthy discussion with Colin Edwards at Schatt in Vancouver, once again I was reminded something that seems easy in theory gets complicated in reality.
We would have had to replace the winch and drum to accommodate the different freeboard which was OK, but it was the freeboard at the maximum list required by rules. My head was spinning at the end of that call and I had a page of indecipherable notes. It always pays to do your homework before you spend money on the engineering.